Some hard drives are designed with the assumption that significant movement of the drive may occur while the hard drive is operating. As such, hard drives may include measures to compensate for shock and vibration that may occur during operation. For example, in a multi-drive configuration such as a disk array, the cooling fans as well as the drives themselves may generate vibrations that may be transmitted between hard drives through the structure in which they are mounted.
One type of vibration seen in drives is known as rotational vibration (RV), which is a twisting/torqueing type action. Rotational vibration is measured as an angular rate of change, e.g., radians per second. If RV is not taken into account in the design of the drive, the force of RV can push the head off track causing missed revolutions and delays in data transfers. Tests on drives not capable of handling RV have shown significant reductions in performance in the presence of RV.